Inhibition of endothelin receptors in the treatment of pulmonary arterial hypertension: does selectivity matter?

Rapid separation and binding configuration prediction of the components in Danshen decoction to endothelin A receptor using affinity chromatography and molecular dynamics simulation

As a famous traditional Chinese formula, Danshen Decoction has the potential to relieve the pain of pulmonary arterial hypertension patients, however, the functional components remain unknown. Herein, we reported a method to screen the functional components in Danshen Decoction targeting endothelin receptor A, an accepted target for the treatment of the disease. The receptor was functionalized on the macroporous silica gel through an epidermal growth factor receptor fusion tag and its covalent inhibitor. Using the affinity gel as the stationary phase, the bioactive compound was identified as salvianolic acid B by mass spectrometry. The binding kinetic parameter (dissociation rate constants k_d ) of salvianolic acid B with the receptor was determined via peak profiling. Using the specific ligands of the receptor as probes, the binding configuration prediction of salvianolic acid B with the receptor was performed by molecular dynamics simulation. Our results indicated that salvianolic acid B is a potential bioactive compound in Danshen Decoction targeting the receptor. This work showed that receptor chromatography in combination with molecular dynamics simulation is applicable to predicting the binding kinetics and configuration of a ligand to a receptor, providing crucial insight for the rational design of drugs that recognize functional proteins.

Endothelin A receptor antagonist attenuated renal iron accumulation in iron overload heme oxygenase-1 knockout mice

Progressive iron accumulation and renal impairment are prominent in both patients and mouse models of sickle cell disease (SCD). Endothelin A receptor (ETA) antagonism prevents this iron accumulation phenotype and reduces renal iron deposition in proximal tubules of SCD mice. To better understand the mechanisms of iron metabolism in the kidney and the role of ETA receptor in iron chelation and transport, we studied renal iron handling in a non-sickle cell iron overload model, heme oxygenase-1 (Hmox-1-/-) knockout mice. We found that Hmox-1-/- mice had elevated plasma endothelin-1 (ET-1), cortical ET-1 mRNA expression, and renal iron content compared to Hmox-1+/+ controls. The ETA receptor antagonist, ambrisentan, attenuated renal iron deposition, without any changes to anemia status in Hmox-1-/- mice. This was accompanied by reduced urinary iron excretion. Finally, ambrisentan had an important iron recycling effect by increasing expression of cellular iron exporter, ferroportin-1 (FPN-1) and circulating total iron levels in Hmox-1-/- mice. These findings suggest the ET-1/ETA signaling pathway contributes to in renal iron trafficking in a murine model of iron overload.

Chronic ETA antagonist reverses hypertension and impairment of structure and function of peripheral small arteries in aortic stiffening

Arterial stiffness may contribute to the pathogenesis of hypertension. The goal of this study is to elucidate the role of Endothelin-1 (ET-1) in aortic stiffening-induced hypertension through ET_A receptor activation. An increase in aortic stiffness was created by use of a non-constrictive restraint, NCR on the abdominal aortic surface. A group of rats underwent aortic NCR or sham operation for 12 weeks and were then treated with ET_A receptor antagonist BQ-123 for 3 weeks. We found that 12 weeks of aortic NCR significantly increased pulse and mean pressure and altered peripheral flow pattern, accompanied by an increased serum ET-1 level (p < 0.05). The increase in aortic stiffness (evidenced by an elevated pulse wave velocity) caused hypertrophic structural remodeling and decreased arterial compliance, along with an impaired endothelial function in peripheral small arteries. BQ-123 treatment only partially attenuated peripheral arterial hypertrophy and restored arterial compliance, but completely recovered endothelium function, and consequently restored local flow and lowered blood pressure. Our findings underscore the hemodynamic coupling between aortic stiffening and peripheral arterial vessels and flow dynamics through an ET_A-dependent mechanism. ET_A receptor blockade may have therapeutic potential for improving peripheral vessel structure and function in the treatment of aortic stiffness-induced hypertension.

Concise Review: Tissue Engineering of Urinary Bladder; We Still Have a Long Way to Go?

Regenerative medicine is a new branch of medicine based on tissue engineering technology. This rapidly developing field of science offers revolutionary treatment strategy aimed at urinary bladder regeneration. Despite many promising announcements of experimental urinary bladder reconstruction, there has been a lack in commercialization of therapies based on current investigations. This is due to numerous obstacles that are slowly being identified and precisely overcome. The goal of this review is to present the current status of research on urinary bladder regeneration and highlight further challenges that need to be gradually addressed. We put an emphasis on expectations of urologists that are awaiting tissue engineering based solutions in clinical practice. This review also presents a detailed characteristic of obstacles on the road to successful urinary bladder regeneration from urological clinician perspective. A defined interdisciplinary approach might help to accelerate planning transitional research tissue engineering focused on urinary tracts. Stem Cells Translational Medicine 2017;6:2033-2043.

[Bosentan use in pulmonary arterial hypertension: Russian and foreign experience]

The results of evaluating the efficacy and safety of bosentan in patients with pulmonary arterial hypertension (PAH), as shown by the data of foreign randomized controlled trials and the authors' own experience, convincingly demonstrate that the introduction of the drug into clinical practice has led to a significant improvement of the possibilities of drug therapy in patients with this serious illness. Bosentan substantially improves physical activity in patients, reduces the severity of clinical symptoms, slows down the rates of disease progression, and prolongs survival in patients with different forms of PAH.

Functional estimation of endothelin-1 receptor antagonism by bosentan, macitentan and ambrisentan in human pulmonary and radial arteries in vitro

BACKGROUND

Endothelin receptor antagonists are approved for pulmonary arterial hypertension. Development of selective ET_A-receptor antagonists over mixed or dual receptor antagonists has depended on a range of receptor binding assays, second messenger assays and functional blood vessel assays. This study compared the 3 clinically-approved endothelin receptor antagonists in assays of human isolated pulmonary and radial arteries in vitro.

METHODS

Human isolated pulmonary (i.d. 5.5mm) and human radial (i.d. 3.23mm) artery ring segments were mounted in organ baths for isometric force measurement. Single concentration-contraction curves to endothelin-1 were constructed in the absence or presence of bosentan (1-10µM), macitentan (0.03-0.3µM) or ambrisentan (0.1-1µM).

RESULTS

All 3 endothelin antagonists caused competitive rightward shifts in the endothelin-1 concentration-response curves in both arteries. The Clark plot and analysis gave the following pK_B values: bosentan, pulmonary artery 6.28±0.13 and radial artery 6.04±0.10; macitentan, pulmonary artery 8.02±0.13 and radial artery 7.49±0.08; and ambrisentan, pulmonary artery 7.38±0.13 and radial artery 6.96±0.10.

CONCLUSIONS

Noting the maximum plasma levels attained from recommended oral doses of each antagonist in volunteers, the pK_B findings here show that there would be significant antagonism of endothelin-1 contraction in the pulmonary and radial arteries at therapeutic plasma levels. This functional assay confirms in human tissue that much higher plasma concentrations of endothelin-1 receptor antagonists are required to be effective than those predicted from binding or other biochemical assays.

Long-Term Endothelin-A Receptor Antagonism Provides Robust Renal Protection in Humanized Sickle Cell Disease Mice

Sickle cell disease (SCD)-associated nephropathy is a major source of morbidity and mortality in patients because of the lack of efficacious treatments targeting renal manifestations of the disease. Here, we describe a long-term treatment strategy with the selective endothelin-A receptor (ET_A) antagonist, ambrisentan, designed to interfere with the development of nephropathy in a humanized mouse model of SCD. Ambrisentan preserved GFR at the level of nondisease controls and prevented the development of proteinuria, albuminuria, and nephrinuria. Microscopy studies demonstrated prevention of podocyte loss and structural alterations, the absence of vascular congestion, and attenuation of glomerulosclerosis in treated mice. Studies in isolated glomeruli showed that treatment reduced inflammation and oxidative stress. At the level of renal tubules, ambrisentan treatment prevented the increased excretion of urinary tubular injury biomarkers. Additionally, the treatment strategy prevented tubular brush border loss, diminished tubular iron deposition, blocked the development of interstitial fibrosis, and prevented immune cell infiltration. Furthermore, the prevention of albuminuria in treated mice was associated with preservation of cortical megalin expression. In a separate series of identical experiments, combined ET_A and ET_B receptor antagonism provided only some of the protection observed with ambrisentan, highlighting the importance of exclusively targeting the ET_A receptor in SCD. Our results demonstrate that ambrisentan treatment provides robust protection from diverse renal pathologies in SCD mice, and suggest that long-term ET_A receptor antagonism may provide a strategy for the prevention of renal complications of SCD.

Effect of treatment with iloprost with or without bosentan on nailfold videocapillaroscopic alterations in patients with systemic sclerosis

INTRODUCTION

Vascular involvement plays a decisive role in systemic sclerosis (SSc) pathogenesis; it is responsible for some important clinical manifestations of the disease such as Raynaud's phenomenon and digital ulcers (DU). Bosentan, a dual receptor endothelin antagonist, and iloprost, often in combination therapy, seems to be able to interfere with the scleroderma microangiopathy.

OBJECTIVES

Aim of the study was to evaluate the effect of bosentan and iloprost on scleroderma microangiopathy, analyzed by means of capillaroscopic skin ulcer risk index (CSURI), in SSc patients treated for the prevention of DU.

METHODS

Nailfold videocapillaroscopy (NVC) was performed in 95 SSc patients, treated with iloprost alone (group 1) or combination therapy with iloprost and bosentan (group 2), at baseline and after one year. In all patients CSURI was calculated according to the formula "diameter × number of megacapillaries/(total number of capillaries)²": in addition, total number of capillaries, giant capillaries, micro-hemorrhages, disorganization of the vascular array, and ramified capillaries were evaluated by means of a semiquantitative score.

RESULTS

After 12 months, we observed a reduction of the number of giant capillaries in both groups, while an increase of ramified capillaries was recorded only in group 2. CSURI improved slightly in group 2 without statistical significance; on the contrary, in group 1 a significant worsening was recorded (p ≤ 0.001).

CONCLUSIONS

Our study confirms the effectiveness of bosentan, in combination with iloprost, in SSc microangiopathy observed to NVC. Moreover, the observed findings further support the role of CSURI in the evaluation and monitoring of SSc microangiopathy.

Potential beneficial role for endothelin in scleroderma vasculopathy: inhibition of endothelial apoptosis by type B endothelin-receptor signaling

Objectives

Microvascular endothelial cell (MVEC) apoptosis is considered to be a key event in the pathogenesis of systemic sclerosis (SSc), an increased expression of endothelin-1 (ET1) is also well recognized in the disease. ET1 is thought to exert deleterious effects on the vasculature by virtue of its known vasospastic, proliferative and fibrotic effects, yet ET1 can act as a survival factor for a variety of cells, including MVEC. The aim of this study is to investigate if ET1 signaling protects SSc-MVECs from apoptosis.

Methods

The expression levels of ET1-receptor genes: Endothelin Receptor Type A gene (EDNRA) and Endothelin Receptor Type B gene (EDNRB), and the effects of selective Endothelin Receptor Type A (ETA) antagonists, selective Endothelin Receptor Type B (ETB), and dual ETA/B antagonist in the presence and/or absence of ET1 on control and SSc-MVEC apoptosis were examined.

Results

Significant increase in the expression of ETA and ETB was noted in SSc-MVECs. Growth factors withdrawal (GFW) resulted in a significant apoptosis that was considerably reduced by the addition ET1. The addition of ETA-receptor antagonists did not affect ET1 anti-apoptotic effects, while the nonselective ETA/B or the selective ETB-receptor antagonists blocked the anti-apoptotic effects of ET1. Finally, an upregulation of the proapoptotic gene BAX after GFW was noted that was normalized by the addition of ET1.

Conclusions

The results suggest that ET1 mediates an anti-apoptotic effect through engaging the ETB receptors in MVECs. Therefore, it appears that selective ETA antagonism may have an advantage over the non-selective ET1-receptor antagonists in SSc vasculopathy, particularly in the early stages of the disease when MVEC apoptosis is rampant.

Endothelin

The endothelins comprise three structurally similar 21-amino acid peptides. Endothelin-1 and -2 activate two G-protein coupled receptors, ETA and ETB, with equal affinity, whereas endothelin-3 has a lower affinity for the ETA subtype. Genes encoding the peptides are present only among vertebrates. The ligand-receptor signaling pathway is a vertebrate innovation and may reflect the evolution of endothelin-1 as the most potent vasoconstrictor in the human cardiovascular system with remarkably long lasting action. Highly selective peptide ETA and ETB antagonists and ETB agonists together with radiolabeled analogs have accurately delineated endothelin pharmacology in humans and animal models, although surprisingly no ETA agonist has been discovered. ET antagonists (bosentan, ambrisentan) have revolutionized the treatment of pulmonary arterial hypertension, with the next generation of antagonists exhibiting improved efficacy (macitentan). Clinical trials continue to explore new applications, particularly in renal failure and for reducing proteinuria in diabetic nephropathy. Translational studies suggest a potential benefit of ETB agonists in chemotherapy and neuroprotection. However, demonstrating clinical efficacy of combined inhibitors of the endothelin converting enzyme and neutral endopeptidase has proved elusive. Over 28 genetic modifications have been made to the ET system in mice through global or cell-specific knockouts, knock ins, or alterations in gene expression of endothelin ligands or their target receptors. These studies have identified key roles for the endothelin isoforms and new therapeutic targets in development, fluid-electrolyte homeostasis, and cardiovascular and neuronal function. For the future, novel pharmacological strategies are emerging via small molecule epigenetic modulators, biologicals such as ETB monoclonal antibodies and the potential of signaling pathway biased agonists and antagonists.

Endothelin receptors and their antagonists

All three members of the endothelin (ET) family of peptides, ET-1, ET-2, and ET-3, are expressed in the human kidney, with ET-1 being the predominant isoform. ET-1 and ET-2 bind to two G-protein–coupled receptors, ET_A and ET_B, whereas at physiological concentrations ET-3 has little affinity for the ET_A receptor. The human kidney is unusual among the peripheral organs in expressing a high density of ET_B. The renal vascular endothelium only expresses the ET_B subtype and ET-1 acts in an autocrine or paracrine manner to release vasodilators. Endothelial ET_B in kidney, as well as liver and lungs, also has a critical role in scavenging ET-1 from the plasma. The third major function is ET-1 activation of ET_B in in the nephron to reduce salt and water re-absorption. In contrast, ET_A predominate on smooth muscle, causing vasoconstriction and mediating many of the pathophysiological actions of ET-1. The role of the two receptors has been delineated using highly selective ET_A (BQ123, TAK-044) and ET_B (BQ788) peptide antagonists. Nonpeptide antagonists, bosentan, macitentan, and ambrisentan, that are either mixed ET_A/ET_B antagonists or display ET_A selectivity, have been approved for clinical use but to date are limited to pulmonary hypertension. Ambrisentan is in clinical trials in patients with type 2 diabetic nephropathy. This review summarizes ET-receptor antagonism in the human kidney, and considers the relative merits of selective versus nonselective antagonism in renal disease.

The molecular targets of approved treatments for pulmonary arterial hypertension

Until recently, three classes of medical therapy were available for the treatment of pulmonary arterial hypertension (PAH)--prostanoids, endothelin receptor antagonists and phosphodiesterase type 5 (PDE5) inhibitors. With the approval of the soluble guanylate cyclase stimulator riociguat, an additional drug class has become available targeting a distinct molecular target in the same pathway as PDE5 inhibitors. Treatment recommendations currently include the use of all four drug classes to treat PAH, but there is a lack of comparative data for these therapies. Therefore, an understanding of the mechanistic differences between these agents is critical when making treatment decisions. Combination therapy is often used to treat PAH and it is therefore important that physicians understand how the modes of action of these drugs may interact to work as complementary partners, or potentially with unwanted consequences. Furthermore, different patient phenotypes mean that patients respond differently to treatment; while a certain monotherapy may be adequate for some patients, for others it will be important to consider alternating or combining compounds with different molecular targets. This review describes how the four currently approved drug classes target the complex pathobiology of PAH and will consider the distinct target molecules of each drug class, their modes of action, and review the pivotal clinical trial data supporting their use. It will also discuss the rationale for combining drugs (or not) from the different classes, and review the clinical data from studies on combination therapy.

Protective effects of endothelin receptor A and B inhibitors against doxorubicin-induced cardiomyopathy

The clinical efficiency of the highly potent antitumor agent doxorubicin is limited by cardiotoxic effects. In a murine doxorubicin cardiotoxicity model, increased endothelin-1 (ET-1) expression and cardioprotective effects of the dual ET-1 blocker bosentan were demonstrated. To date it is unclear if combined blocking of endothelin A/B receptors is necessary or whether selective inhibition of one of the ET-1 receptors is sufficient for the observed cardioprotection. Therefore, we investigated the impact of dual (bosentan) and single endothelin receptor antagonism through sitaxentan (receptor A blocker) or BQ788 (receptor B blocker) in a murine doxorubicin cardiotoxicity model (C57BL/6N). Simultaneous administration of each endothelin receptor antagonist (ERA) with doxorubicin resulted in a significantly improved hemodynamic performance in comparison to the impaired cardiac function in control mice with bosentan being most effective but closely followed by sitaxentan and also BQ788. This cardioprotection was not caused by diminished doxorubicin levels in heart since the doxorubicin content in cardiac tissue was not altered by ERAs significantly. However, whole transcript expression profiling showed partly different effects of the ERAs on doxorubicin-modulated cardiac gene expression of genes involved in signal transduction (e.g. Stat3, Pim1, Akt1, Plcb2), fibrosis (e.g. Myl4), energy production (e.g. Ant1) or oxidative stress (e.g. Aox1). Furthermore, doxorubicin-mediated gene regulations were verified in the murine cardiomyocyte model HL-1 showing partly reversed expression patterns after co-administration of the ERAs. In summary, our results demonstrate strong cardioprotective effects of blocking ET-1 receptors against the doxorubicin-related cardiomyopathy and provide evidence to potential underlying signaling pathways.

Selective endothelin-A receptor blockade attenuates endotoxin-induced pulmonary hypertension and pulmonary vascular dysfunction

Endothelin-1 is a potent mediator of sepsis-induced pulmonary hypertension (PH). The pulmonary vascular effects of selective blockade of endothelin receptor subtype A (ETAR) during endotoxemia remain unknown. We hypothesized that selective ETAR antagonism attenuates endotoxin-induced PH and improves pulmonary artery (PA) vasoreactivity. Adult male Sprague-Dawley rats (250-450 g) received lipopolysaccharide (LPS; Salmonella typhimurium; 20 mg/kg intraperitoneally) or vehicle 6 hours before hemodynamic assessment and tissue harvest. The selective ETAR antagonist sitaxsentan (10 or 20 mg/kg) or vehicle was injected intravenously 3 hours after receipt of LPS. Right ventricular systolic pressure, mean arterial pressure (MAP), cardiac output (CO), oxygenation (P/F ratio), and serum bicarbonate were measured. Bronchoalveolar lavage (BAL) cell differential and lung wet-to-dry ratios were obtained. Endothelium-dependent and endothelium-independent vasorelaxations were determined in isolated PA rings. PA interleukin (IL)-1β, IL-6, tumor necrosis factor α (TNF-α), and inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) were measured. LPS caused PH, decreased MAP, CO, and serum bicarbonate, and increased PA IL-1β, IL-6, TNF-α, and iNOS mRNA. Sitaxsentan attenuated sepsis-induced PH and increased MAP. The P/F ratio, CO, serum bicarbonate, and BAL neutrophilia were not affected by sitaxsentan. In isolated PA rings, while not affecting phenylephrine-induced vasocontraction or endothelium-dependent relaxation, sitaxsentan dose-dependently attenuated LPS-induced alterations in endothelium-independent relaxation. PA cytokine mRNA levels were not significantly attenuated by ETAR blockade. We conclude that ETAR blockade attenuates endotoxin-induced alterations in systemic and PA pressures without negatively affecting oxygenation. This protective effect appears to be mediated not by attenuation of sepsis-induced cardiac dysfunction, acidosis, or alveolar inflammation but rather by improved endothelium-independent vasorelaxation.

The role of endothelin-1 in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare but debilitating disease, which if left untreated rapidly progresses to right ventricular failure and eventually death. In the quest to understand the pathogenesis of this disease differences in the profile, expression and action of vasoactive substances released by the endothelium have been identified in patients with PAH. Of these, endothelin-1 (ET-1) is of particular interest since it is known to be an extremely powerful vasoconstrictor and also involved in vascular remodelling. Identification of ET-1 as a target for pharmacological intervention has lead to the discovery of a number of compounds that can block the receptors via which ET-1 mediates its effects. This review sets out the evidence in support of a role for ET-1 in the onset and progression of the disease and reviews the data from the various clinical trials of ET-1 receptor antagonists for the treatment of PAH.

Effect of ambrisentan on peripheral circulation in patients with systemic sclerosis

Systemic sclerosis (SSc) is characterized by disturbed blood circulation. The effect of ambrisentan, an endothelin-A receptor-selective antagonist, on impaired peripheral circulation in SSc remains largely elusive. Here we show SSc patients, whose clinical symptoms such as cyanosis and Raynaud's phenomenon, were ameliorated by the treatment with ambrisentan. Additionally, objective evaluations with thermography showed improvement of hand coldness in steady-state and cold challenge tests. Ambrisentan might have a potential to improve peripheral circulation in SSc.

Rosiglitazone Attenuated Endothelin-1-Induced Vasoconstriction of Pulmonary Arteries in the Rat Model of Pulmonary Arterial Hypertension via Differential Regulation of ET-1 Receptors

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by a progressive increase in pulmonary arterial pressure leading to right ventricular failure and death. Activation of the endothelin (ET)-1 system has been demonstrated in plasma and lung tissue of PAH patients as well as in animal models of PAH. Recently, peroxisome proliferator-activated receptor γ (PPARγ) agonists have been shown to ameliorate PAH. The present study aimed to investigate the mechanism for the antivasoconstrictive effects of rosiglitazone in response to ET-1 in PAH. Sprague-Dawley rats were exposed to chronic hypoxia (10% oxygen) for 3 weeks. Pulmonary arteries from PAH rats showed an enhanced vasoconstriction in response to ET-1. Treatment with PPARγ agonist rosiglitazone (20 mg/kg per day) with oral gavage for 3 days attenuated the vasocontractive effect of ET-1. The effect of rosiglitazone was lost in the presence of _L-NAME, indicating a nitric oxide-dependent mechanism. Western blotting revealed that rosiglitazone increased ET_BR but decreased ET_AR level in pulmonary arteries from PAH rats. ET_BR antagonist A192621 diminished the effect of rosiglitazone on ET-1-induced contraction. These results demonstrated that rosiglitazone attenuated ET-1-induced pulmonary vasoconstriction in PAH through differential regulation of the subtypes of ET-1 receptors and, thus, provided a new mechanism for the therapeutic use of PPARγ agonists in PAH.

Inhibition of vascular endothelial growth factor receptor under hypoxia causes severe, human-like pulmonary arterial hypertension in mice: potential roles of interleukin-6 and endothelin

AIMS

Severe pulmonary arterial hypertension (PAH) is an incurable disease whose exact mechanisms remain unknown. However, growing evidence highlights the role of inflammation and endothelin (ET) signaling. The lack of reliable models makes it difficult to investigate the pathophysiology of this disease. Our aim was therefore to develop a mouse model of severe PAH closely mimicking the human condition to explore the role of interleukin-6 (IL-6), and ET signaling in advanced PAH progression.

MAIN METHODS

Young male SV129 mice received vascular endothelial growth factor receptor inhibitor (SU5416) three times a week and were exposed to hypoxia (10% O2) for three weeks. Molecular analysis and histological assessment were examined using real-time PCR, Western blot and immunostaining, respectively.

KEY FINDINGS

The developed murine model presented important characteristics of severe PAH in human: concentric neointimal wall thickening, plexogenic lesions, recruitment of macrophages, and distal arteriolar wall muscularization. We detected an increase of IL-6 production and a stronger macrophage recruitment in adventitia of remodeled arterioles developing plexogenic lesions. Moreover, ET-1 and ET receptor A were up-regulated in lung lysates and media of remodeled arterioles. Recombinant IL-6 stimulated the proliferation and regulated endothelial cells in increasing ET-1 and decreasing ET receptor B.

SIGNIFICANCE

These data describe a murine model, which displays the most important features of human severe PAH. We assume that inflammation, particularly IL-6 regulating ET signaling, plays a crucial role in forming plexogenic lesions. This model is thus reliable and might be used for a better understanding of severe PAH progression and treatment.

Clinical safety, pharmacokinetics, and efficacy of ambrisentan therapy in children with pulmonary arterial hypertension

Recent trials in adult PAH revealed the efficacy of ambrisentan. However, in children with PAH, the clinical safety and pharmacokinetics of ambrisentan has not been well studied. Our aim was to investigate the clinical safety, pharmacokinetics, tolerability, and efficacy of endothelin receptor antagonist therapy with ambrisentan in children with pulmonary arterial hypertension (PAH). This retrospective cohort study provides clinical data from pediatric patients with PAH receiving ambrisentan as add-on therapy or transition from bosentan. Safety included evaluation of adverse events including aminotransferase abnormalities. The clinical impact was evaluated by improvement from baseline in clinical variables. A total of 38 pediatric patients with PAH received ambrisentan. Fifteen of 38 patients were switched from bosentan to ambrisentan. The remaining 23 children were treated with ambrisentan as an add-on therapy due to disease progression. In both transition and add-on cases, mean pulmonary artery pressure significantly improved (transition; 55 ± 18 vs. 45 ± 20 mmHg, n = 13, P = 0.04, add-on; 52 ± 17 vs. 45 ± 19 mmHg, n = 13, P = 0.03) during the follow-up. World Health Organization functional class improved in 31% of patients, but one patient required an atrial septostomy due to disease progression during the follow-up period (median, range; 20, 4-44 months). Five patients (13%) discontinued ambrisentan due to severe headache, lack of clinical efficacy, or near syncope. Ten patients (26%) had side effects associated with ambrisentan treatment, including nasal congestion, headache, and flushing. However, no patients had aminotransferase abnormalities and there were no deaths after initiation of ambrisentan during follow-up. Pharmacokinetics were evaluated in sixteen children treated with ambrisentan from 2.5 mg to 10.0 mg; the mean peak plasma concentration was 738 ± 452 ng/ml, mean time to peak plasma concentration was 3.2 ± 2.1 hours, and mean area under the curve plasma concentration was 6657 ± 4246 ng·hour/ml. In conclusion, initial experience with ambrisentan in children suggests that treatment is safe with similar pharmacokinetics to those in adults and may improve PAH in some children.

Peroxisome proliferator-activated receptor-γ ameliorates pulmonary arterial hypertension by inhibiting 5-hydroxytryptamine 2B receptor

An elevated plasma level of 5-hydroxytryptamine (5-HT) or upregulation of 5-HT receptor signaling or both is implicated in vascular contraction and remodeling in pulmonary arterial hypertension (PAH). Recently, peroxisome proliferator-activated receptor-γ (PPARγ) agonists have been shown to ameliorate PAH. However, their effects on the 5-HT-induced contraction of pulmonary arteries remain unknown. Here, we examined the role of PPARγ in inhibiting 5-HT2B receptor (5-HT2BR) to ameliorate PAH. Pulmonary arteries from PAH rats induced by monocrotaline or chronic hypoxia showed an enhanced vasoconstriction in response to BW723C86, a specific agonist for 5-HT2BR. Expression of 5-HT2BR was also increased in pulmonary arteries from the PAH rats, accompanied by vascular remodeling and right ventricular hypertrophy. Treatment with the PPARγ agonist rosiglitazone in vivo reversed the expression and the vasocontractive effect of 5-HT2BR as well as the thickening of pulmonary arteries. In pulmonary artery smooth muscle cells, 5-HT induced the gene expression of 5-HT2BR, which was inhibited by rosiglitazone, pioglitazone, or adenovirus-mediated overexpression of constitutively activated PPARγ. The pharmacological effect of PPARγ was through the suppression of the 5-HT-induced activator protein-1 activity. These results demonstrated the beneficial effect of PPARγ on 5-HT2BR-mediated vasocontraction, providing a new mechanism for the potential use of PPARγ agonists in PAH.

The pharmacological treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening and progressive disease of various origins characterized by pulmonary vascular remodeling that leads to increased pulmonary vascular resistance and pulmonary arterial pressure, most often resulting in right-sided heart failure. The most common symptom at presentation is breathlessness, with impaired exercise capacity as a hallmark of the disease. Advances in understanding the pathobiology over the last 2 decades have led to therapies (endothelin receptor antagonists, phosphodiesterase type 5 inhibitors, and prostacyclins or analogs) initially directed at reversing the pulmonary vasoconstriction and more recently directed toward reversing endothelial cell dysfunction and smooth muscle cell proliferation. Despite these advances, disease progression is common even with use of combination regimens targeting multiple mechanistic pathways. Overall 5-year survival for PAH has increased significantly from approximately 30% in the 1980s to approximately 60% at present, yet remains abysmal. This review summarizes the mechanisms of action, clinical data, and regulatory histories of approved PAH therapies and describes the latest agents in late-stage clinical development.

Vascular endothelin receptor type B: structure, function and dysregulation in vascular disease

Endothelin-1 (ET-1) is a major regulator of vascular function, acting via both endothelin receptor type A (ET(A)R) and type B (ET(B)R). Although the role of ET(A)R in vascular smooth muscle (VSM) contraction has been studied, little is known about ET(B)R. ET(B)R is a G-protein coupled receptor with a molecular mass of ~50 kDa and 442 amino acids arranged in seven transmembrane domains. Alternative splice variants of ET(B)R and heterodimerization and cross-talk with ET(A)R may affect the receptor function. ET(B)R has been identified in numerous blood vessels with substantial effects in the systemic, renal, pulmonary, coronary and cerebral circulation. ET(B)R in the endothelium mediates the release of relaxing factors such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, and could also play a role in ET-1 clearance. ET(B)R in VSM mediates increases in [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other pathways of VSM contraction and cell growth. ET-1/ET(A)R signaling has been associated with salt-sensitive hypertension (HTN) and pulmonary arterial hypertension (PAH), and ET(A)R antagonists have shown some benefits in these conditions. In search for other pathogenetic factors and more effective approaches, the role of alterations in endothelial ET(B)R and VSM ET(B)R in vascular dysfunction, and the potential benefits of modulators of ET(B)R in treatment of HTN and PAH are being examined. Combined ET(A)R/ET(B)R antagonists could be more efficacious in the management of conditions involving upregulation of ET(A)R and ET(B)R in VSM. Combined ET(A)R antagonist with ET(B)R agonist may need to be evaluated in conditions associated with decreased endothelial ET(B)R expression/activity.

Sunitinib-Induced Systemic Vasoconstriction in Swine Is Endothelin Mediated and Does Not Involve Nitric Oxide or Oxidative Stress

Angiogenesis inhibition with agents targeting tyrosine kinases of vascular endothelial growth factor receptors is an established anticancer treatment, but is, unfortunately, frequently accompanied by systemic hypertension and cardiac toxicity. Whether vascular endothelial growth factor receptor antagonism also has adverse effects on the pulmonary and coronary circulations is presently unknown. In chronically instrumented awake swine, the effects of the vascular endothelial growth factor receptor antagonist sunitinib on the systemic, pulmonary, and coronary circulation were studied. One week after sunitinib (50 mg PO daily), mean aortic blood pressure (MABP) had increased from 83±5 mm Hg at baseline to 97±6 mm Hg ( P <0.05) because of a 57±20% increase in systemic vascular resistance as cardiac output decreased. In contrast, sunitinib had no discernible effects on pulmonary and coronary hemodynamics or cardiac function. We subsequently investigated the mechanisms underlying the sunitinib-induced systemic hypertension. Intravenous administration of NO synthase inhibitor N G -nitro- l -arginine increased MABP by 24±1 mm Hg under baseline conditions, whereas it increased MABP even further after sunitinib administration (32±3 mm Hg; P <0.05). Reactive oxygen species scavenging with a mixture of antioxidants lowered MABP by 13±2 mm Hg before but only by 5±2 mm Hg ( P <0.05) after sunitinib administration. However, intravenous administration of the dual endothelin A/endothelin B receptor blocker tezosentan, which did not lower MABP at baseline, completely reversed MABP to presunitinib values. These findings indicate that sunitinib produces vasoconstriction selectively in the systemic vascular bed, without affecting pulmonary or coronary circulations. The sunitinib-mediated systemic hypertension is principally attributed to an increased vasoconstrictor influence of endothelin, with no apparent contributions of a loss of NO bioavailability or increased oxidative stress.

Ambrisentan

Ambrisentan, an orally active, highly selective antagonist of the endothelin-1 type A receptor, is indicated for the treatment of pulmonary arterial hypertension (PAH). It has a low potential for drug-drug interactions and requires only once-daily administration. Three months' treatment with ambrisentan 2.5-10 mg/day significantly improved exercise capacity, as determined by the distance walked in 6 minutes (6MWD; primary outcome measure), compared with placebo in two double-blind, multicenter studies in patients with PAH (ARIES-1 [n = 202] and -2 [n = 192]). A decrease in dyspnea and a delay in clinical worsening were among the improvements in secondary outcomes generally observed with ambrisentan versus placebo. In ARIES-E, a 2-year extension of ARIES-1 and -2, approved dosages of ambrisentan (5 and 10 mg/day) were associated with a sustained improvement in 6MWD, a generally sustained improvement in dyspnea, and a low risk of clinical worsening and of death. Six months' treatment with ambrisentan 5 mg/day significantly improved 6MWD (primary outcome measure) and dyspnea relative to baseline in an open-label, non-comparative, multicenter study in a diverse population of patients with PAH or non-PAH forms of pulmonary hypertension (ARIES-3 [n = 224]). Ambrisentan was associated with a low risk of clinical worsening and of death. Ambrisentan treatment was generally well tolerated in the various ARIES trials. All available pre-registration and post-marketing data indicate the drug poses only a very low risk of liver injury; the 'black box' warning regarding potential liver injury has been removed from the US prescribing information for ambrisentan.

Endothelin receptor antagonists -- their role in pulmonary medicine

INTRODUCTION

Understanding of the function of endothelin-1 in the pathophysiology of endothelial disease, in particular pulmonary arterial hypertension (PAH), has paved the way for the development of endothelin-receptor antagonists (ERAs) and explains the leading role they now play in the treatment armamentarium for this disease.

BACKGROUND

Three active ERA drugs (bosentan, sitaxentan, ambrisentan) are currently approved for the treatment of PAH in France. Several randomised clinical trials have demonstrated their efficacy and safety in PAH.

PERSPECTIVES AND CONCLUSION

Besides its vasoconstrictor effect, endothelin-1 (ET-1) plays a pivotal role in cell proliferation and apoptosis. ERAs are innovative drugs potentially useful in some pulmonary disorders such as idiopathic pulmonary fibrosis or systemic sclerosis, even though the preliminary results published remain insufficient or controversial.

CONCLUSION

ERAs play a major role in the management of pulmonary vascular disease. Other drugs, still under study, could prove useful in the treatment of infiltrating pneumonias.

Protective effects of endothelin-A receptor antagonist BQ123 against LPS-induced oxidative stress in lungs

The aim of this study was to assess whether endothelin-A receptor (ET(A)-R) blocker, BQ123, influences lung edema, lipid peroxidation TBARS), hydrogen peroxide (H(2)O(2)), TNF-α concentration or the glutathione redox system in the lung homogenates obtained from LPS-induced endotoxic shock rats. The study was performed on male Wistar rats (n = 6 per group) divided into groups: (1) saline, (2) LPS (15 mg/kg)-saline, (3) BQ123 (0.5 mg/kg)-LPS, (4) BQ123 (1 mg/kg)-LPS. The ET(A)-R antagonist was injected intravenously 30 min before LPS administration. Five hours after saline or LPS administration, animals were sacrificed and lungs were isolated for indices of lung edema, oxidative stress and TNF-α concentration. Injection of LPS alone resulted in lung edema development and a marked increase in TNF-α (p < 0.02), TBARS (p < 0.02), and H(2)O(2) (p < 0.01) concentrations as well as a depletion of total glutathione (p < 0.01). Administration of BQ123 (1 mg/kg), before LPS challenge, led to a significant reduction in TNF-α and H(2)O(2) concentrations (p < 0.05) and elevation of both total glutathione and the GSH/GSSG ratio (p < 0.05). However, it did not prevent LPS-induced TBARS increase and lung edema formation. Interestingly, a lower dose of BQ123 was much more effective in decreasing H(2)O(2), TBARS, as well as TNF-α levels (p < 0.02, p < 0.05, p < 0.05, respectively). That dose was also effective in prevention of lung edema development (p < 0.01). Taken together, the obtained results indicate that BQ123 is highly effective in decreasing LPS-induced oxidative stress in lungs. Moreover, the dose of 0.5 mg/kg of the antagonist showed to be more effective in decreasing free radical generation and lung edema in endotoxemic rats.

Treatment of pulmonary arterial hypertension with targeted therapies

Pulmonary arterial hypertension (PAH) is a rare disorder characterized by progressive obliteration of the pulmonary microvasculature that results in elevated pulmonary vascular resistance and premature death. Although no cure exists for PAH, improved understanding of the pathobiological mechanisms of this disease has resulted in the development of effective therapies that target specific aberrant pathways. Agents that modulate abnormalities in the prostacyclin, endothelin, and nitric oxide pathways have been shown in randomized, controlled studies to confer improvements in functional status, pulmonary hemodynamics, and possibly even slow disease progression. Several additional pathways believed to play an important role in the pathogenesis of PAH have been identified as potentially useful therapeutic targets and a number of investigative approaches focusing on these targets are in active development. In this Review, we highlight the pharmacological agents currently available for the treatment of PAH and discuss potential novel strategies.

Insights into ET(A) subtype selectivity of benzodiazepine endothelin receptor antagonists by 3D-QSAR approaches

ET(A) subtype selective antagonists constitute a novel and potentially important class of agents for the treatment of pulmonary hypertension, heart failure, and other pathological conditions. In this paper, 60 benzodiazepine derivatives displaying potent activities against ET(A) and ET(B) subtypes of endothelin receptor were selected to establish the 3D-QSAR models using CoMFA and CoMSIA approaches. These models show excellent internal predictability and consistency, external validation using test-set 19 compounds yields a good predictive power for antagonistic potency. Statistical parameters of models were obtained with CoMFA-ET(A) (q (2) = 0.787, r (2) = 0.935, r (2) ( pred ) = 0.901), CoMFA-ET(B) (q (2) = 0.842, r (2) = 0.984, r (2) ( pred ) = 0.941), CoMSIA-ET(A) (q (2) = 0.762, r (2) = 0.971, r (2) ( pred ) = 0.958) and CoMSIA-ET(B) (q (2) = 0.771, r (2) = 0.974, r (2) ( pred ) = 0.953) respectively. Field contour maps (CoMFA and CoMSIA) corresponding to the ET(A) and ET(B) subtypes reflects the characteristic similarities and differences between these types. The results of this paper provide valuable information to facilitate structural modifications of the title compounds to increase the inhibitory potency and subtype selectivity of endothelin receptor.

Macitentan: entry-into-humans study with a new endothelin receptor antagonist

Purpose

To study the pharmacokinetics, pharmacodynamics, and tolerability of rising single doses of macitentan, an endothelin receptor antagonist, in healthy male subjects.

Methods

This double-blind, placebo-controlled study was performed in seven groups of eight healthy male subjects. Doses of 0.2, 1, 5, 25, 100, 300 and 600 mg or placebo (two subjects per group) were administered. Plasma macitentan and endothelin-1 and serum total bile salt concentrations were measured and analysed non-compartmentally. Plasma and urine were analysed qualitatively for the presence of metabolites and one of these, ACT-132577, was also measured quantitatively in plasma. Standard tolerability measurements were performed throughout the study.

Results

Macitentan was slowly absorbed and, at a dose of 300 mg, the t_1/2 (95% confidence interval, CI) was 17.5 h (14.1, 21.8). The dose-proportionality coefficient β for C_max (95% CI) was 0.83 (0.79, 0.87) indicating less than dose-proportional pharmacokinetics of macitentan. In plasma, a pharmacologically active oxidative depropyl metabolite, ACT-132577, was found whereas in urine two minor metabolites were detected. The t_1/2 of ACT-132577 (95% CI) was 65.6 h (53.1, 80.9). Macitentan dose-dependently increased endothelin-1 concentrations up to 2.2-fold (95% CI 1.4, 2.4) at a dose of 600 mg, but had no consistent effect on total bile salts. Macitentan was well tolerated up to and including a dose of 300 mg, the maximum tolerated dose. Headache, nausea and vomiting were dose-limiting adverse events.

Conclusion

The pharmacokinetic and tolerability profile of macitentan is consistent with a once-a-day dosing regimen and warrants further investigation in clinical studies.

Prevention of bronchial hyperreactivity in a rat model of precapillary pulmonary hypertension

BACKGROUND

The development of bronchial hyperreactivity (BHR) subsequent to precapillary pulmonary hypertension (PHT) was prevented by acting on the major signalling pathways (endothelin, nitric oxide, vasoactive intestine peptide (VIP) and prostacyclin) involved in the control of the pulmonary vascular and bronchial tones.

METHODS

Five groups of rats underwent surgery to prepare an aorta-caval shunt (ACS) to induce sustained precapillary PHT for 4 weeks. During this period, no treatment was applied in one group (ACS controls), while the other groups were pretreated with VIP, iloprost, tezosentan via an intraperitoneally implemented osmotic pump, or by orally administered sildenafil. An additional group underwent sham surgery. Four weeks later, the lung responsiveness to increasing doses of an intravenous infusion of methacholine (2, 4, 8 12 and 24 μg/kg/min) was determined by using the forced oscillation technique to assess the airway resistance (Raw).

RESULTS

BHR developed in the untreated rats, as reflected by a significant decrease in ED50, the equivalent dose of methacholine required to cause a 50% increase in Raw. All drugs tested prevented the development of BHR, iloprost being the most effective in reducing both the systolic pulmonary arterial pressure (Ppa; 28%, p = 0.035) and BHR (ED50 = 9.9 ± 1.7 vs. 43 ± 11 μg/kg in ACS control and iloprost-treated rats, respectively, p = 0.008). Significant correlations were found between the levels of Ppa and ED50 (R = -0.59, p = 0.016), indicating that mechanical interdependence is primarily responsible for the development of BHR.

CONCLUSIONS

The efficiency of such treatment demonstrates that re-establishment of the balance of constrictor/dilator mediators via various signalling pathways involved in PHT is of potential benefit for the avoidance of the development of BHR.

Effect of transition from sitaxsentan to ambrisentan in pulmonary arterial hypertension

Introduction:

Currently available endothelin receptor antagonists for treating pulmonary arterial hypertension block either the endothelin (ET) receptor A or both A and B receptors. Transition from one endothelin receptor antagonist to another may theoretically alter side-effects or efficacy. We report our experience of a transition from sitaxsentan to ambrisentan, both predominant ET_A receptor antagonists, in pulmonary arterial hypertension patients.

Methods:

At Baylor Pulmonary Hypertension Center, 18 patients enrolled in the open-label extension phase of the original sitaxsentan studies (Sitaxsentan To Relieve ImpaireD Exercise) were transitioned to ambrisentan (from July 2007 to September 2007) at the time of study closure. Pre-transition (PreT), 1 month (1Mth) and 1 year (1Yr) post-transition assessments of 6-minute walk distance (6MWD), brain naturetic peptide (BNP) levels, WHO functional class (WHO FC), Borg dyspnea score (BDS), oxygen saturation, liver function, and peripheral edema were compared.

Results:

6MWD was 356 ± 126 m at PreT, 361 ± 125 m at 1Mth, and 394 ± 114 m at 1Yr (mean ± SD). There was no difference in the walk distance at 1Mth and 1Yr post transition compared with PreT (P = 0.92, 0.41 respectively). Oxygen saturation was no different at 1Mth and 1Yr to PreT level (P = 0.49 and P = 0.06 respectively). BNP was 178 ± 44 pg/mL at PreT, 129 ± 144 pg/mL at 1Mth and 157 ± 201 at 1Yr. Peripheral edema was present in 7/18 patients at PreT, in 8/16 patients at 1Mth, and in 6/13 patients at 1Yr post transition. Proportions of patients with edema over these 3 time points did not change significantly (P = 0.803). At 1Yr, 2 patients had died, 1 had undergone lung transplantation, 1 had relocated, and 1 patient was started on intravenous prostacyclin therapy. Over 3 points (baseline, 1 month, and 1 year), there was no significant change in function class (P = 0.672).

Conclusion:

Our limited data suggest that ET_A receptor antagonists can be switched from one to another with sustained exercise capacity and maintained WHO FC with no increase in incidence of peripheral edema.

Endothelin receptor antagonists for pulmonary arterial hypertension: an overview

The last decade has seen major advances in the pharmacotherapy of pulmonary arterial hypertension (PAH). One of these advances has been the discovery of endothelin receptor antagonists (ERAs). ERAs are a class of potent vasodilators and antimitotic substances, which could specifically dilate and remodel pulmonary arterial system, and have been proposed as an alternative to traditional therapies for PAH. Current available evidence suggests that ERAs improve exercise capacity, functional status, pulmonary hemodynamics, and delay the time to clinical worsening for patients with PAH. This review attempts to provide an overview of the pharmacology, therapeutic benefits, and safety profile of ERAs in patients with PAH.

Inhibition of endothelin-1 and hypoxia-induced pulmonary pressor responses in the rat by a novel selective endothelin-A receptor antagonist, di-n-butylaminocarbamyl-L-leucyl-D-tryptophanyl-D-4-chloro-Phe

Pulmonary hypertension is a kind of disease associated with a very high rate of mortality, and there are not many effective drugs for the treatment. Today, endothelin (ET)-1 receptor antagonists were proved to be effective in the treatment of pulmonary hypertension. Aiming at developing new endothelin-A receptor (ETA) antagonist for treatment of pulmonary hypertension, di-n-butylaminocarbamyl-L-leucyl-D-tryptophanyl-D-4-chloro-Phe, named GF063, was synthesized at base of selective ETA receptor antagonist BQ485 and selected for the further pharmacological characterization. The preliminary pharmacodynamics of GF063 was evaluated by radioligand receptor binding assay and test of antivasoconstriction effects in vitro and in vivo. The integrative pharmacodynamics was evaluated in hypoxia-induced rat pulmonary hypertension. In vitro, GF063 bound to ETA receptor with 100,000-fold higher affinity than to ETB receptor. GF063 concentration dependently inhibited contraction of isolated rat aortic ring induced by ET-1 and shifted the cumulative concentration-contraction response curve to right with no change in the maximal response. In vivo, GF063 inhibited the increase of mean systemic arterial pressure induced by ET-1 in anesthetized rat. In hypoxia-induced rat pulmonary hypertension model, pretreatment with GF063 (40 mg/kg, s.c.) significantly decreased pulmonary artery pressure and right ventricular hypertrophy, also significantly inhibited the increase of ET-1 level in lung, improved hemodynamics, and alleviated the wall thickness of pulmonary vessels. This study indicated that GF063, as a selective ETA receptor antagonist, could inhibit vasoconstriction effects in vivo and in vitro, could prevent pulmonary hypertension induced by hypoxia, and may have great potential to be developed as a new drug of antipulmonary hypertension.

Bosentan for the treatment of adult pulmonary hypertension

Pulmonary hypertension is a severe progressive disease with a marked morbidity and a high mortality attributed to right heart failure. Bosentan, a dual endothelin receptor antagonist, is an effective and well-tolerated oral therapy for the management of pulmonary arterial hypertension (PAH; WHO group 1 pulmonary hypertension). Bosentan improves cardiopulmonary hemodynamics, exercise capacity, WHO functional class and quality of life, as well as delaying time to clinical worsening in patients with PAH. This article reviews the role of endothelin-1 in the pathogenesis and progression of PAH, the diagnosis of PAH and the pharmacology of bosentan, and summarizes the current available evidence for the safety and efficacy of bosentan for the treatment of PAH as a monotherapy and combination therapy, as well as its role in the management of other forms of pulmonary hypertension.

Targeted oral therapies in the treatment of pulmonary arterial hypertension

Recent advances in our understanding of the pathophysiology of pulmonary arterial hypertension (PAH) have led to the US FDA's approval of eight drugs for its treatment. Although guidelines for the use of PAH therapies are available and regularly updated, there is a lack of information on how these agents differ and what characteristics may enable one agent to be of greater relative clinical utility than another. Oral agents may be compared across a variety of measures, including clinical efficacy, safety and tolerability, dosing and pharmacology, potential for drug interactions, treatment adherence and suitability for use in combination regimens. Although no large, prospective, head-to-head trial has been conducted with oral agents for PAH, data from placebo-controlled studies indicate that the enrolled patient populations were remarkably homogeneous with respect to demographic and disease severity parameters. In general, data suggest that these agents improve functional capacity, delay disease progression and improve haemodynamics. Additionally, long-term sustainability of response has been demonstrated. However, there was no consistently superior agent across the primary and secondary endpoints assessed in these trials, and the magnitudes of improvements were in a fairly defined range across agents. Consequently, treatment choice may shift to other aspects such as drug safety and tolerability, potential for drug interactions, dosing convenience, treatment adherence, effect on quality of life and access to medication. In this review, the four targeted oral agents approved for the treatment of PAH in the US are reviewed, and clinical results are placed into context.

Current and future therapeutic options for persistent pulmonary hypertension in the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is a potentially life-threatening condition that is characterized by supra-systemic pulmonary vascular resistance causing right-to-left shunting through the ductus arteriosus and/or foramen ovale, leading to a vicious cycle of hypoxemia, acidosis and further pulmonary vasoconstriction. Advances in neonatology including surfactant instillation, high-frequency ventilation, extracorporeal membrane oxygenation and, most importantly, inhaled nitric oxide (INO), have revolutionized the management of PPHN. However, given that INO does not improve oxygenation in a significant proportion (30-40%) of cases, there is an urgent need to consider other therapeutic options for PPHN. The issue is more important for developing nations with a higher PPHN-related health burden and limited resources. This article discusses the evidence about INO in term and preterm neonates in brief, and focuses mainly on the potential alternative drugs in the management of PPHN.

Adult patients with pulmonary arterial hypertension due to congenital heart disease: a review on advanced medical treatment with bosentan

Pulmonary arterial hypertension (PAH) is a progressive disease with poor survival outcome. PAH is classified by the 2009 updated clinical classification of pulmonary hypertension and a major subgroup is PAH due to congenital heart disease (CHD) with systemic-to-pulmonary shunt. CHD-PAH is a result of systemic-to-pulmonary shunting and chronic increased flow that ultimately results in adaptations of pulmonary vasculature and endothelial dysfunction. The advanced stage is called Eisenmenger syndrome which forms a small percentage (1%) of all CHD patients. Therapies targeted on PAH symptoms are called primary therapy for PAH, but most CHD-PAH patients progress to advanced therapy which is directed at the PAH itself. In CHD-PAH, advanced therapies are extensively investigated for all three major pathways: endothelin-1 receptor antagonists such as bosentan, prostanoids such as epoprostenol and phosphodiesterase 5 inhibitors such as sildenafil. Endpoints in most trials were catheterization hemodynamics, World Health Organization functional class, six-minute walking distance and patient-focused outcomes, based on quality of life questionnaires and Borg dyspnea index. The BREATHE-5 and EARLY study were two important randomized controlled trials showing efficacy of bosentan at short follow-up. Moreover in patients with Eisenmenger syndrome, one recent survival retrospective study with majority of patients on bosentan showed strong survival benefit over conservative therapy. A diversity of prospective cohort and retrospective studies were performed but all with limited data, due to small numbers and heterogeneity of underlying CHD diagnoses. Further larger studies are needed to determine optimal treatment for adults with CHD-PAH. This review focuses on bosentan in CHD-PAH. In particular, we discuss outcome of various clinical trials and compare efficacy and safety of bosentan to other advanced therapies.

Safety and efficacy of ambrisentan for the treatment of portopulmonary hypertension

BACKGROUND

Ambrisentan is a selective endothelin-receptor antagonist that is approved by the US Food and Drug Administration for the treatment of pulmonary arterial hypertension. We describe hemodynamic responses and clinical outcomes of patients with portopulmonary hypertension (POPH) treated with ambrisentan.

METHODS

In this observational study, we prospectively identified and followed consecutive adult patients with POPH who received monotherapy with ambrisentan ≤ 10 mg daily from January 2007 until December 2009. Liver enzymes were assessed monthly. Pulmonary hemodynamic responses were assessed using echocardiograms and right-sided heart catheterizations.

RESULTS

We identified 13 patients (seven men) with POPH and began monotherapy with ambrisentan. The median age was 57 (interquartile range [IQR], 52-60). Patients were followed for a median of 613 days (IQR, 385-1,011). The median model for end-stage liver disease score was 10 (IQR, 8.5-15); eight patients had Child-Turcotte-Pugh A classification. Median time on ambrisentan therapy was 390 days (IQR, 363-611). Two patients died, one of advanced hepatocellular carcinoma and one of septic shock following pneumonia. The mean pulmonary artery pressure decreased from a baseline median of 58 mm Hg (IQR, 37-63) to 41 mm Hg (IQR, 27-48) (P = .004). The pulmonary vascular resistance median was reduced from 445 dynes/s/cm(5) (IQR, 329-834) to 174 dynes/s/cm(5) (IQR, 121-361) (P = .008). There was no difference in the longitudinal analysis of liver function tests (aspartate aminotransferase, alanine aminotransferase, total bilirubin, and international normalized ratio) after 12 months of therapy. One patient underwent successful liver transplantation and normalized pulmonary hemodynamic responses after transplantation.

CONCLUSIONS

In this small cohort of patients with moderate to severe pulmonary hypertension in the setting of POPH, we have shown that ambrisentan monotherapy can significantly improve pulmonary hemodynamic responses without adverse effect on hepatic function.

Darusentan, a selective endothelin A receptor antagonist, for the oral treatment of resistant hypertension

Resistant hypertension is defined as failure to lower blood pressure to target when a patient adheres to the maximum tolerated doses of three antihypertensive drugs including a diuretic. Notwithstanding the wide availability of several antihypertensive agents and the continued recommendation of dietary and lifestyle modifications, the prevalence of resistant hypertension remains high and is expected to increase thus underscoring the need for potential new treatment modalities in resistant hypertension. Endothelin-1 is a long-lasting potent vasoconstrictor and plays a key role in cardiovascular haemostasis. Endothelin mediates its biological activity in humans through the endothelin A and B receptors. The clinical experience and the evidence for therapy with darusentan in resistant systemic hypertension are reviewed. The leading journals that publish basic science and clinical research in the area of cardiovascular diseases and PubMed were scanned. While results from early clinical studies suggested that darusentan might emerge as new treatment option in patients with resistant hypertension, results from recent studies suggests that darusentan appears unlikely to find its way in the armamentarium for treatment of resistant hypertension.